Morphine and Apomorphine Inhibit Gastrointestinal Transit [GIT] Through Two Different Mechanisms

ABSTRACT

Morphine was used as a remedy for the control of diarrhea centuries before it's sedative-analgesic effect was discovered. Although several mechanisms have been proposed for the morphine-induced inhibition of gastrointestinal transit [GIT], the exact mechanism has not yet been identified. On this basis the possible involvement of the dopaminergic system in morphine-induced inhibition of transit was investigated. This study showed that morphine decreased gastrointestinal transit [GIT] of charcoal dust in mice in a dose-dependent manner. The response was inhibited by the opiate antagonist naloxone. Pretreatment of animals with the D-2 antagonist sulpiride or the peripheral dopamine antagonist domperidone did not alter the morphine-induced inhibition of GIT. The D-l/D-2 agonist apomorphine also decreased GIT in mice. The response was inhibited by SCH 23390 or sulpiride pretreatment [p<0.01], but not by domperidone or naloxone. It is concluded that morphine and apomorphine inhibit GIT through opiate and dopaminergic mechanisms, respectively